Gold nanoparticles are one of the most widely used classes of nanomaterials for chemical, bioanalytical, biomedical, optical and nanotechnological applications. While numerous methods are known for the synthesis of gold nanoparticles, the ability to control the size, shape and monodispersity of such gold nanoparticles is one of the most important areas for the targeted applications. This is because the electronic, optical, and chemical/biological properties exploited in these applications are highly dependent on the size, shape and size monodispersity of the nanoparticles. Few standard protocols have been established to allow preparation of gold nanoparticles of the desired sizes, shapes and high monodispersity in a systematic way. Such ability is critical for the targeted applications.
One method of the prior art for providing size monodispersed nanoparticles involves forming polydispersed nanoparticles using a variety of techniques known to those of skill in the art. Nanoparticles of a selected size range may then be selected from the polydispersed population using an instrument such as a differential mobility analyzer (DMA). Because the size resolution of a typical DMA is only about 10%, the degree of size monodispersity of the selected nanoparticles is similarly low.
Other techniques are known to those skilled in the art. Prior art techniques generally provide populations of gold nanoparticles in the size range of 2 to 30 nm diameter having best case size monodisperities of approximately 5-10%.
The present invention, however, provides a nanoparticle production technique that involves seeded growth of gold nanoparticles to form almost any desired size in the range of approximately 30-90 nm diameters. Nanoparticles formed in accordance with the inventive method exhibit size monodispersity having as small as a 2% relative standard deviation. This is significantly better than methods of the prior art for at least two reasons. First, highly size monodispersed nanoparticles having any desired diameter in the range of approximately 30-90 nm may be repeatably formed. This provides size control not heretofore available. Second, as previously mentioned, size monodisperity with relative standard deviations as low as 2% are achieved using the method of the invention.